Hi! Do you know how to spell 'Prosecco'?" These are the first words Brie Larson says when she jumps on the phone, calling somewhere from deep in the heart of London. She has been doing interviews all day and has a screening later in the evening, and though the 26-year-old actress could not sound more chipper, she's already thinking ahead to the meal that awaits her in a few hours. "There's a nice, long dinner in my future, so I'm mapping out my drink order." Asked if she's planning on getting her beverage delivered to her hotel suite, Larson lets out a noise that sounds like a cross between reverb-heavy guffaw and a gunshot. "No, we're definitely going to a restaurant. I can actually leave my room to eat now!"

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Anyone who's familiar with the premise of Room, the big-screen adaptation of Emma Donoghue's bestselling novel, would not blame the actress for wanting to get out a bit. The story of a kidnapped young woman held captive with her son (played by seven-year-old Jacob Tremblay), Larson spends much of the film playing, arguing, sleeping, crying, laughing, plotting — and yes, eating — inside a domicile only slightly bigger than a proverbial bread box. But in Irish director Lenny Abrahamson's hands, what might have been another Lifetime channel tearjerker is carefully molded into a tender, touching and nervewrackingly tense story — a combination that, along with Room's two central performances, has turned this modest drama into a left-field festival hit and a buzzed-about Oscar contender.

According to Donoghue, the idea of writing about parenthood had been on her mind when she happened to stumble across a news story about Elisabeth Fritzl, an Austrian woman who had been imprisoned in a basement and raped by her father for decades. "I was right in the maelstrom of motherhood when I first heard about it," she says. "My children were four and one and a half, and I was going through that phase where you constantly feel like you're being broken and remade by the experience of raising kids. So when this story came across my radar, I thought: A locked room would be a great way to shine a bright spotlight on the everyday heroism of being a parent — from the limitations and boredom as well as the magical moments. It just took things to an immediate extreme."

After the book was published in 2010, it was shortlisted for the Man Booker Prize and showed up on a number of year-end best-of lists. By the time President Barack Obama was photographed in Martha's Vineyard carrying the hardcover edition in 2011, Room was already a bestseller — and had made its way to Abrahamson, best known for directing the Michael-Fassbender-sings-under-a-giant-paper-mâché-head dramedy Frank. "I was so taken with everything about it, just as a reader," the director says. "But I immediately knew how I'd turn it into a movie. Then I saw that picture of Obama walking out of the bookstore with it, and I thought, 'Well, the fucking cat's out of the bag now, I have no chance in hell of making it. I look forward to seeing what Mr. Spielberg does with this.'"

On a whim, however, Abrahamson decided to send a 10-page fan letter to Donoghue, telling her how much he loved the book and and how it felt it should be filmed. Unbeknownst to him, the author had written a screenplay for Room shortly after she'd sold the novel — a way of ensuring she stay involved just in case she was ever approached by producers. Donoghue was surprised that he not only understood the book "frighteningly well" but his ideas were perfectly in sync with her script. "The key to adapting something isn't to take a clock apart and rebuild it," she says. "It's taking a clock apart and turning it into a kettle. You throw away the bits a kettle wouldn't need and find the ones it would, and Lenny got that. He ended the letter by saying 'Please trust me with your movie.' I was just blown away by that.

"The first time we met," she continues, "I mentioned that his previous films are beautiful, but someone tends to die in all of them! So I asked him, 'Are you going to kill anyone off? And are you going to keep in the breastfeeding?' He said no, and yes. [There is indeed a brief, slightly veiled reference to it in the film.] I told them that he needed to put music in it as well. Once he agreed, we were set."

Jacob Tremblay, on the set of 'Room.'George Kraychyk courtesy of A24

The duo began meeting regularly, brainstorming on how to translate the story for the screen. The book's notion of presenting the narrative through the eyes of Jack, the five-year-old boy — "You allow the victim to set the terms, not the psychopath," Donoghue says, regarding that first-person perspective — wouldn't work for a movie; it would need to become more of a two-hander, in which both Ma and her son were given equal weight. Shortly after they began to draw up a list of actresses who might be right for the mother's part, a woman in Abrahamson's office brought up a film she'd seen the previous weekend. "She said, 'Oh, I've just seen this lovely American film called Short Term 12, you should check it out,'" he says. "So I watched it, and 90 minutes later, Brie Larson very quickly shot to the top of the list. This was someone who was very present, very controlled — and who clearly would not have a problem bonding with a little boy."

As for Larson, she'd been turned on to the book by her manager, who'd given her a copy of Room with the caveat, "Enjoy, but someone very famous will be getting this part...so maybe don't picture yourself in it." When the 21 Jump Street actress heard a year later that a script was making the rounds, she said she'd made peace with the fact that "I wasn't even going to be in the running to be in the running for it." Abrahamson says that during her audition, "she was confident enough to say, Yeah, I don’t know what's going work here, but what about this…and then she'd try one way, then another, and then another after that. I just thought, 'Oh, this works. She's making this feel like play, like a discovery. This will be good.'"

Once Larson got the role, she began talking to a trauma specialist at USC about the effects of sexual abuse. Then she initiated a self-imposed "social blackout," in which she mostly stayed in her apartment, keeping interactions with family and friends to a bare minimum. She also hired a personal trainer, going to the gym daily while maintaining a strict diet. That last part seems confusing — getting in great shape to play someone trapped in a 10 x 10 room — until Larson explains that, without a physical transformation, she simply would not have been able to play the role.

"Part of it was because Ma had such little food available to her," the actress says, "I wanted to look malnourished. But when I was talking to a nutritionist and having him look over my blood work, he told me that 'You can't just eat less than you're eating now…you have zero muscle mass on you! You won't be able to function.' So there was a practical reason behind lifting a few weights. Plus when we coming up with a backstory for her, I knew she was an athlete before she'd been abducted. She would have been keeping active and moved around a lot, even if she was stuck in a small room.

"I saw that picture of Obama walking out of the bookstore with Room, and I thought, 'Well, the fucking cat's out of the bag now. I look forward to seeing what Mr. Spielberg does with this.'"-Lenny Abrahamson

"But because I'd never really had muscle mass before," Larson adds, "my body started to change chemically. I started to have more testosterone, so suddenly I had this fury…this anger and this strength that I had never tapped into before. It quickly became less about how the character looked physically and more about how it made me feel mentally. I could not have played Ma without that."

While she was prepping to get in the mindset of the protective matriarch, the production team started its search for the young actor who'd play Jack — a process that they'd purposely saved for the last possible minute. "I was already nervous about finding a child for the part," Donoghue admits, "because when I was writing the screenplay, I didn't hold back on giving him a lot of lines. You can't make his role smaller. But Lenny kept telling me, don't worry, the kid is out there. We just can't get him too early or by the time we film, he'll have grown up!"

"You have no film without that boy, so yes: We were incredibly worried," Abrahamson says, laughing. "We whittled it down from literally hundreds and hundreds of candidates to just a few — and then up pops Jacob Tremblay, with this huge engine of an actor inside this seven-year-old body."

Brie Larson and Jacob Tremblay, in a scene from 'Room.'George Kraychyk

Larson remembers that, during their initial meeting over pizza, she and the shy young actor made small talk over Star Wars figurines; by the end of the evening, they were building Teenage Mutant Ninja Turtle sets with Legos back at his house and slowly starting to bond. "Out of the blue, he began asking me questions very seriously: What's my favorite color? What's my favorite animal? I started getting nervous. Am I answering wrong? Was he judging me?!? What I found out later was that someone told him it was my birthday in a couple of days, and he wanted to get me a present." There's a pause on the other end of the line. "So I now have a mug with a red panda on it."

Staying in the same apartment building and sharing a 45-minute ride every morning to Room's production offices in Toronto, Larson and Tremblay began to develop a strong us-against-the-world rapport. When they got to the actual room that would serve as their characters home/prison, the two would sit on the set and engage in what Larson describes as a sort of territorial pissing. "We'd usually spend a couple of hours in the room — not filming stuff, just playing and getting used to the space," she says. "We would draw portraits of each other and make things; all those toys you see in the film, we built. Sometimes, Lenny would sit in and call out something, an event or chore that would be part of the characters' day-to-day routine, and we'd do that. But usually, he'd leave us in there by ourselves, and we'd just talk and hang out. We were making the place ours."

And since Larson was almost always the one closest to the person she calls "this little bouncing energy of light," the actress was the one who'd by taking care of Jacob's immediate needs, from asking for bathroom breaks to simply entertaining him between shots. By the time "action" was called, the two had forged something that resembled a real parent-child relationship. And when the film eventually switches its focus from incarceration to dealing with PTSD, Larson claims that Tremblay greatly helped her remains stable and grounded when her character begins to fall apart.

"For Ma, Jack becomes this constant living reminder of this horrible thing she endured. For me, Jake was a constant reminder that this is not real."-Brie Larson

"Those scenes were tougher than the earlier ones," she says, noting that they movie was shot virtually in chronological order. "When you're suffering repeated sexual trauma" — her character is raped by their captor, "Old Nick," on a nightly basis — "and are forced to live in that small a space, your body basically keeps from breaking down by shutting down. But let's say you removed yourself from that environment all of a sudden; everything would go back online, so to speak, and suddenly, you're dealing with years of repressed agony and despair all at once.

"The first half of the movie is about Jacob," she continues, "but the second half is about Ma and how she deals with what she went through. It required going to some painful places. But Jacob just sees it all as play; we're just having fun. So it made it very easy when he's around to not go to any place that's too dark. For Ma, Jack becomes this constant living reminder of this horrible thing she endured. For me, Jake was a constant reminder that this is not real. The darkness frequency just flies over his head."

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For Donoghue and Abrahamson, the near-rapturous reception that Room has received since premiering at the Telluride Film Festival last September feels like both the end of a long journey and, in their words, the beginning of a "deserved recognition phase" for their actors. As for Larson, she could not be prouder that the movie is sparking such intense conversation, particularly in regards to what the real-life victims of such crimes go through.

"I felt a strong responsibility not just to tell this story, but to tell it right," she says, sounding remarkably solemn. Then she lets out a long weary sigh, before unleashing another loud, reverb-y laugh. "But at the moment, I have a responsibility to make sure I get to this screening on time and get a glass of Prosecco before this night is over."